Activation during preparation of therapeutic platelets affects deterioration during storage: a comparative flow cytometric study of different production methods

Heterogeneity of platelets and their responses

There has been increasing recognition of heterogeneity in blood platelets and their responses, particularly in recent years, where next-generation technologies and advanced bioinformatic tools that interrogate "big data" have enabled large-scale studies of RNA and protein expression across a growing list of disease states. However, pioneering platelet biologists and clinicians were already hypothesizing upon and investigating heterogeneity in platelet (and megakaryocyte) activity and platelet metabolism and aggregation over half a century ago. Building on their foundational hypotheses, in particular Professor Marian A. Packham's pioneering work and a State of the Art lecture in her memoriam at the 2023 International Society on Thrombosis and Haemostasis Congress by Anandi Krishnan, this review outlines the key features that contribute to the heterogeneity of platelets between and within individuals. Starting with important epidemiologic factors, we move stepwise through successively smaller scales down to heterogeneity revealed by single-cell technologies in health and disease. We hope that this overview will urge future scientific and clinical studies to recognize and account for heterogeneity of platelets and aim to apply methods that capture that heterogeneity. Finally, we summarize other exciting new data presented on this topic at the 2023 International Society on Thrombosis and Haemostasis Congress.

Cold stored platelets in the management of bleeding: is it about bioenergetics?

When platelet concentrates (PCs) were first introduced in the 1960s as a blood component therapy, they were stored in the cold. As platelet transfusion became more important for the treatment of chemotherapy-induced thrombocytopenia, research into ways to increase supply intensified. During the late 1960s/early 1970s, it was demonstrated through radioactive labeling of platelets that room temperature platelets (RTP) had superior post-transfusion recovery and survival compared with cold-stored platelets (CSP). This led to a universal switch to room temperature storage, despite CSP demonstrating superior hemostatic effectiveness upon being transfused. There has been a global resurgence in studies into CSP over the last two decades, with an increase in the use of PC to treat acute bleeding within hospital and pre-hospital care. CSP demonstrate many benefits over RTP, including longer shelf life, decreased bacterial risk and easier logistics for transport, making PC accessible in areas where they have not previously been, such as the battlefield. In addition, CSP are reported to have greater hemostatic function than RTP and are thus potentially better for the treatment of bleeding. This review describes the history of CSP, the functional and metabolic assays used to assess the platelet storage lesion in PC and the current research, benefits and limitations of CSP. We also discuss whether the application of new technology for studying mitochondrial and glycolytic function in PC could provide enhanced understanding of platelet metabolism during storage and thus contribute to the continued improvements in the manufacturing and storage of PC.

Effect of platelet-rich plasma on the attachment of periodontal ligament fibroblasts to the diseased root surface and the attendant collagen formation

OBJECTIVE

To investigate the effect of different concentrations of platelet-rich plasma (PRP) on collagen formation via periodontal ligament fibroblasts (PDLFs) on the surface of demineralised diseased tooth roots.

METHODS

Various PDLFs were grown from tissue explants, with the cells between the fifth and eighth passage in the culture used. Human whole blood obtained from healthy subjects was collected in tubes containing an anticoagulant (acid-citrate-dextrose) and centrifuged (1300 rpm for 10 min) before the supernatant PRP layer was removed. A second spin at (2000 rpm for 10 min) produced the PRP fraction. The effect of PRP of various concentrations on the attachment of PDLFs on the diseased root surface of human teeth demineralised with ethylenediaminetetraacetic acid (EDTA) and treated with the PRP was then investigated in terms of PRP collagen formation, with the formation observed using the Sirius red staining method.

RESULTS

The optical density values of the experimental groups were statistically significantly higher than those of the control groups (P < 0.05), while the Sirius red staining returned positive results for both the experimental group (A) and the control group (B). The images were analysed using a histogram, and a statistically significant difference was found (P < 0.05).

CONCLUSION

While PRP could promote the attachment and collagen formation of PDLFs on the diseased root surface of human teeth demineralised with EDTA and treated with PRP, the effect is potentially reduced when the dose exceeds 20%.

Biotinylated Platelets: A Promising Labeling Technique?

Labeling of platelets (PLTs) is essential for research purposes, in order to measure the recovery and survival of transfused PLTs in vivo. Biotinylation is a promising new alternative to the gold standard of radioactive labeling. This review highlights 4 key publications that provide significant insights into biotin-labeled PLTs (bioPLTs). Stohlawetz et al. established that transfusion of bioPLTs in human recipients is possible. De Bruin et al. developed a standardized, reproducible protocol for biotinylation of PLTs as a promising method to trace and isolate transfused PLTs in vivo, with reduced levels of PLT activation markers. Muret et al. developed a nonwashing biotin labeling method to implement in a blood bank environment. Finally, in a preclinical study, Ravanat et al. showed that different densities of biotin can be used to concurrently monitor multiple populations of human PLTs in the circulation of the same subject. These studies have made major contributions to the development of bioPLTs as a viable option for use in human research, and indicate that bioPLTs can be safely administered, preferably at a low density of biotin.

Assessment of apheresis platelets during 5 days of storage: A National Cancer Institute, Cairo University experience

BACKGROUND

Platelet transfusion therapy is widely used to prevent hemorrhage in patients with thrombocytopenia and platelet disorders. The platelet concentrate (PC) quality is affected by increased storage time, as reflected in the decreased number of platelets, morphological changes, and impaired functions. This study aimed to analyze the impact of 5 days storage on platelets count and the expression of CD63, and Annexin V as activation markers during PC storage.

METHODS

Fifty PCs collected from single donors were tested for platelet count on days 0, 3, and 5 using a Sysmex blood counter. CD61, CD63, and Annexin V expression was analyzed by a multicolor Navios flow cytometer.

RESULTS

There was a significant decrease in platelet count during 5 days of storage. There was a direct relationship between storage time and degree of platelet activation. CD63 had almost double increased expression on day 5 than day 3. Annexin V showed significantly increased expression on day 3 with minor differences between days 3 and 5.

CONCLUSION

According to standard blood bank conditions, PC stored for 5 days showed a degree of in vitro activation as evidenced by CD63 and Annexin V expression, may lead to reduced therapeutic efficacy. Flow cytometry monitoring platelet activation in PC offers a better understanding of the changes during PC storage and may help improve platelet products.

Evaluating apheresis platelets at reduced dose as a contingency measure for extreme shortages

BACKGROUND

The COVID19 pandemic highlights the need for contingency planning in the event of blood shortages. To increase platelet supply, we assessed the operational impact and effect on platelet quality of splitting units prior to storage.

STUDY DESIGN AND METHODS

Using production figures, we modeled the impact on unit numbers, platelet counts, and volumes of splitting only apheresis double donations into three units (yielding ⅔ doses), or all standard dose units in half. To assess quality, eight pools of three ABO/Rh-matched apheresis (Trima Accel) double donations in plasma were split to ⅔ and ½ volumes in both Terumo and Fresenius storage bags. These were irradiated and subject to maximal permitted periods of nonagitation (3 × 8 h) before comparing platelet quality markers (including pH, CD62P expression) to Day 9 of storage.

RESULTS

Splitting all double donations into three predicted inventory expansion of 23% overall whereas halving all standard dose units clearly doubles stock. In our study, ⅔ and ½ doses contained 153 ± 15 × 10⁹ (~138 ml) and 113 ± 11 × 10⁹ (~102 ml) platelets respectively. Following storage, higher pH was observed in ⅔ than in ½ doses and in Terumo compared to Fresenius bags. The higher pH was reflected in better quality markers, including lower CD62P expression. Despite the differences, on Day 8 (of pH monitoring at expiry) all ⅔ doses and most ½ doses were ≥pH 6.4.

CONCLUSION

A strategy to split apheresis platelets in plasma to lower doses is feasible, maintains acceptable platelet quality, and should be considered by blood services in response to extreme shortages.

Emerging gene therapies for enhancing the hemostatic potential of platelets

Platelet transfusions are an integral component of balanced hemostatic resuscitation protocols used to manage severe hemorrhage following trauma. Enhancing the hemostatic potential of platelets could lead to further increases in the efficacy of transfusions, particularly for non-compressible torso hemorrhage or severe hemorrhage with coagulopathy, by decreasing blood loss and improving overall patient outcomes. Advances in gene therapies, including RNA therapies, are leading to new strategies to enhance platelets for better control of hemorrhage. This review will highlight three approaches for creating modified platelets using gene therapies: (i) direct transfection of transfusable platelets ex vivo, (ii) in vitro production of engineered platelets from platelet-precursor cells, and (iii) modifying the bone marrow for in vivo production of modified platelets. In summary, modifying platelets to enhance their hemostatic potential is an exciting new frontier in transfusion medicine, but more preclinical development as well as studies testing the safety and efficacy of these agents are needed.

Treatment of knee osteoarthritic pain with platelet-rich plasma: a systematic review of clinical studies

Introduction: Knee osteoarthritis is a degenerative joint disease that is secondary to degradation of articular cartilage, reformation of subchondral bone through degradation and proliferation as well as presence of synovitis. Materials & methods: This systematic review was conducted and reported as per Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. Results: A total of 30 of the 48 comparators showed statistically significant superiority with platelet-rich plasma (PRP) compared with a control, while the other 16 comparators showed no significant difference between PRP and the comparator. Conclusion: We can only recommend PRP for patients with early-stage osteoarthritis (I or II) and who are aged below 65, based on our findings. Based on the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) recommendations, while studies reviewed were randomized controlled studies, and therefore, high grade, due to variance in imprecision, risk of bias and inconsistency among the 37 studies, it would be reasonable to rate this paper as subjectively moderate.

Platelet storage and functional integrity

Platelet transfusion is a topic of common interest for many specialists involved in patient care, from laboratory staff to clinical physicians. Various aspects make this type of transfusion different from those of other blood components. In this review, the challenges in platelet transfusion practice that are relevant for laboratory colleagues will be discussed, highlighting how the biochemical and structural characteristics of these blood elements directly affect their function and consequently the clinical outcome. More than 1,300 platelet concentrates are transfused in Germany every day, and several types are offered by their respective manufacturers. We describe the technological advances in platelet concentrate production, with a focus on how the storage conditions of platelets can be improved. Laboratory quality assessment procedures for a safe transfusion are discussed in detail. For this purpose, we will refer to the Hemotherapy Directives (Richtlinie Hämotherapie) of the German Medical Association.

Affordable, Reliable Dual-Platform Approach to Quantitating Phosphatidylserine-Exposing Platelets in Platelet Components

OBJECTIVE

To compare the number of phosphatidylserine (PS)-exposing platelets obtained using the dual-platform approach and bead-based flow cytometry.

METHODS

Platelets were enumerated using the ADVIA 2010i instrument (Siemens AG). The numbers and percentages of PS-exposing platelets in 175 platelet products were determined using a FACSCalibur flow cytometer (Becton, Dickinson and Company) and counting beads.

RESULTS

Our results showed good correlation (r2 = 0.96; P <.001) between the PS-exposing platelets obtained using counting beads and the dual-platform approach. The results of Bland-Altman analysis showed a bias of +46,449 cells per µL and a limit of agreement (LOA) from -197,863 to 290,762 cells per µL. Also, 8 measurements (5.0%) revealed a number of PS-exposing platelets outside the LOA ranges. Further, 21 measurements (12.0%) revealed greater than 2-fold changes in the number of PS-exposing platelets.

CONCLUSIONS

The results suggest that the dual-platform approach is affordable and reliable for quantitating PS-exposing platelets as part of monitoring the quality of platelet products.

The Antithrombotic Function of Sphingosine-1-Phosphate on Human Adipose-Stem-Cell-Recellularized Tissue Engineered Vascular Graft In Vitro

Adipose stem cells (ASCs) show potential in the recellularization of tissue engineerined vascular grafts (TEVGs). However, whether sphingosine-1-phosphate (S1P) could further enhance the adhesion, proliferation, and antithrombosis of ASCs on decellularized vascular scaffolds is unknown. This study investigated the effect of S1P on the recellularization of TEVGs with ASCs. Human ASCs were derived from lipoaspirate. Scaffolds were derived from human umbilical arteries (HUAs) with treatment of 0.1% sodium dodecyl sulfate (SDS) for 48 h (decellularized HUAs; DHUAs). The adhesion, proliferation, and antithrombotic functions (kinetic clotting time and platelet adhesion) of ASCs on DHUAs with S1P or without S1P were evaluated. The histology and DNA examination revealed a preserved structure and the elimination of the nuclear component more than 95% in HUAs after decellularizaiton. Human ASCs (hASCs) showed CD29(+), CD73(+), CD90(+), CD105(+), CD31(-), CD34(-), CD44(-), HLA-DR(-), and CD146(-) while S1P-treated ASCs showed marker shifting to CD31(+). In contrast to human umbilical vein endothelial cells (HUVECs), S1P didn't significantly increase proliferation of ASCs on DHUAs. However, the kinetic clotting test revealed prolonged blood clotting in S1P-treated ASC-recellularized DHUAs. S1P also decreased platelet adhesion on ASC-recellularized DHUAs. In addition, S1P treatment increased the syndecan-1 expression of ASCs. TEVG reconstituted with S1P and ASC-recellularized DHUAs showed an antithrombotic effect in vitro. The preliminary results showed that ASCs could adhere to DHUAs and S1P could increase the antithrombotic effect on ASC-recellularized DHUAs. The antithrombotic effect is related to ASCs exhibiting an endothelial-cell-like function and preventing of syndecan-1 shedding. A future animal study is warranted to prove this novel method.

Acoustofluidic separation of cells and particles

Acoustofluidics, the integration of acoustics and microfluidics, is a rapidly growing research field that is addressing challenges in biology, medicine, chemistry, engineering, and physics. In particular, acoustofluidic separation of biological targets from complex fluids has proven to be a powerful tool due to the label-free, biocompatible, and contact-free nature of the technology. By carefully designing and tuning the applied acoustic field, cells and other bioparticles can be isolated with high yield, purity, and biocompatibility. Recent advances in acoustofluidics, such as the development of automated, point-of-care devices for isolating sub-micron bioparticles, address many of the limitations of conventional separation tools. More importantly, advances in the research lab are quickly being adopted to solve clinical problems. In this review article, we discuss working principles of acoustofluidic separation, compare different approaches of acoustofluidic separation, and provide a synopsis of how it is being applied in both traditional applications, such as blood component separation, cell washing, and fluorescence activated cell sorting, as well as emerging applications, including circulating tumor cell and exosome isolation.

Comparison of three commercially available buffy coat pooling sets for the preparation of platelet concentrates

BACKGROUND

A disposable set for platelet concentrate (PC) preparation by the buffy coat method allows pooling of buffy coats, centrifugation and cell separation with in-line leucocyte filtration. This study compares three commercially available pooling sets in combination with INTERCEPT pathogen inactivation (PI).

MATERIALS AND METHODS

Sets for pooling of buffy coats were from Fresenius Kabi (FRE), Macopharma (MAC) and Terumo BCT (TER). Platelet yield, recovery and concentration were compared before and after PI (n = 20). Platelet quality was assessed by annexin V binding, P-selectin expression and PAC1 binding.

RESULTS

The TER pooling set had the highest platelet yield (5·39 ± 0·44 × 1011 ) compared with MAC (4·53 ± 0·77) and FRE (4·56 ± 0·51) prior to PI. This was the result of a significantly higher platelet concentration in the TER storage bag (1·41 ± 0·12 × 106 /μL) compared with MAC (1·18 ± 0·19) and FRE (1·28 ± 0·15). However, the TER platelet content decreased by 15·6% after PI, yielding 4·55 ± 0·47 × 1011 platelets compared with smaller reductions at 9·5% for MAC (4·10 ± 0·69) and 4·4% for FRE (4·36 ± 0·52). None of the individual PC contained >106 leucocytes. The pH in TER PC was lower compared with MAC and FRE caused by a higher lactic acid production rate. Consequently, PAC1 binding after TRAP activation was lowest for TER PC on day 6. P-selectin and annexin V were not different between suppliers.

CONCLUSION

This study demonstrates the added value of evaluating the entire component production process when introducing a new consumable. This study helped to inform a decision on what pooling set is ideally suited for routine implementation taking into account PI.

Platelet Storage Lesions: What More Do We Know Now?

Platelet concentrate (PC) transfusions are a lifesaving adjunct to control and prevent bleeding in cancer, hematologic, surgical, and trauma patients. Platelet concentrate availability and safety are limited by the development of platelet storage lesions (PSLs) and risk of bacterial contamination. Platelet storage lesions are a series of biochemical, structural, and functional changes that occur from blood collection to transfusion. Understanding of PSLs is key for devising interventions that prolong PC shelf life to improve PC access and wastage. This article will review advancements in clinical and mechanistic PSL research. In brief, exposure to artificial surfaces and high centrifugation forces during PC preparation initiate PSLs by causing platelet activation, fragmentation, and biochemical release. During room temperature storage, enhanced glycolysis and reduced mitochondrial function lead to glucose depletion, lactate accumulation, and product acidification. Impaired adenosine triphosphate generation reduces platelet capacity to perform energetically demanding processes such as hypotonic stress responses and activation/aggregation. Storage-induced alterations in platelet surface proteins such as thrombin receptors and glycoproteins decrease platelet aggregation. During storage, there is an accumulation of immunoactive proteins such as leukocyte-derive cytokines (tumor necrosis factor α, interleukin (IL) 1α, IL-6, IL-8) and soluble CD40 ligand which can participate in transfusion-related acute lung injury and nonhemolytic transfusion reactions. Storage-induced microparticles have been linked to enhanced platelet aggregation and immune system modulation. Clinically, stored PCs have been correlated with reduced corrected count increment, posttransfusion platelet recovery, and survival across multiple meta-analyses. Fresh PC transfusions have been associated with superior platelet function in vivo; however, these differences were abrogated after a period of circulation. There is currently insufficient evidence to discern the effect of PSLs on transfusion safety. Various bag and storage media changes have been proposed to reduce glycolysis and platelet activation during room temperature storage. Moreover, cryopreservation and cold storage have been proposed as potential methods to prolong PC shelf life by reducing platelet metabolism and bacterial proliferation. However, further work is required to elucidate and manage the PSLs specific to these storage protocols before its implementation in blood banks.

Comparative assessment of prophylactic transfusions of platelet concentrates obtained by the PRP or buffy-coat methods, in patients undergoing allogeneic hematopoietic stem cell transplantation

OBJECTIVES

Whole blood-derived platelet concentrates can be obtained by the platelet-rich plasma (PRP-PCs) or the buffy-coat (BC-PCs) method. Few studies have shown that BC-PCs display lower in vitro platelet activation, but scarce information exists regarding transfusion efficacy. We have performed a retrospective study assessing platelet transfusion in patients undergoing allogeneic hematopoietic cell transplantation (AHCT) in our clinic, before and after the implementation of BC-PCs.

METHODS

We reviewed clinical records corresponding to 70 PRP-PCs and 86 BC-PCs prophylactic transfusions, which were performed to 55 AHCT patients. Transfusion efficacy was assessed by the 24-h post-transfusion corrected count increment (24-h CCI) and bleeding events. Clinical factors affecting transfusion outcome were also investigated.

RESULTS

Clinical characteristics and the total number of platelet transfusions were similar among groups. Mean donor exposure was 5.8 and 5.0 in each single PRP-PCs and BC-PCs transfusion, respectively (p < 0.01). The 24-h CCI was significantly higher in patients transfused with BC-PCs than in those receiving PRP-PCs (8.3[2.7-13.4] vs. 4.7[1.3-8.1]; p < 0.01). Independent predictors of poor platelet transfusion response included diagnosis other than acute leukemia (HR 8.30; 95% CI 1.96-35.22; p = 0.004), splenomegaly (HR 8.75; 95% CI 2.77-27.60; p < 0.001), graft versus host disease prophylaxis different from cyclosporine A and methotrexate (HR 3.96; 95% CI 1.55-10.14; p = 0.004) and PRP-PCs transfusion (HR 4.54; 95% CI 1.72-12.01; p = 0.002). There were no differences between both groups regarding the bleeding events.

CONCLUSION

In the AHCT setting, we hypothesize that BC-PCs transfusion, when compared to PRP-PCs, results in higher CCI and reduced donor exposure, but provides no significant benefit regarding bleeding outcome.

A portable system for processing donated whole blood into high quality components without centrifugation

Background

The use of centrifugation-based approaches for processing donated blood into components is routine in the industrialized world, as disparate storage conditions require the rapid separation of ‘whole blood’ into distinct red blood cell (RBC), platelet, and plasma products. However, the logistical complications and potential cellular damage associated with centrifugation/apheresis manufacturing of blood products are well documented. The objective of this study was to evaluate a proof-of-concept system for whole blood processing, which does not employ electromechanical parts, is easily portable, and can be operated immediately after donation with minimal human labor.

Methods and findings

In a split-unit study (n = 6), full (~500mL) units of freshly-donated whole blood were divided, with one half processed by conventional centrifugation techniques and the other with the new blood separation system. Each of these processes took 2–3 hours to complete and were performed in parallel. Blood products generated by the two approaches were compared using an extensive panel of cellular and plasma quality metrics. Comparison of nearly all RBC parameters showed no significant differences between the two approaches, although the portable system generated RBC units with a slight but statistically significant improvement in 2,3-diphosphoglyceric acid concentration (p < 0.05). More notably, several markers of platelet damage were significantly and meaningfully higher in products generated with conventional centrifugation: the increase in platelet activation (assessed via P-selectin expression in platelets before and after blood processing) was nearly 4-fold higher for platelet units produced via centrifugation, and the release of pro-inflammatory mediators (soluble CD40-ligand, thromboxane B2) was significantly higher for centrifuged platelets as well (p < 0.01).

Conclusion

This study demonstrated that a simple, passive system for separating donated blood into components may be a viable alternative to centrifugation—particularly for applications in remote or resource-limited settings, or for patients requiring highly functional platelet product.

Acoustophoretic purification of platelets: feasibility and impact on platelet activation and function

Purity, limited platelet activation, and preservation of platelet function are important stakes of preparation of platelet concentrates (PC) for clinical use. In fact, contaminating red blood cells and leukocytes, as well as activated and/or poorly functional platelets in PC, represents a risk of poor efficiency and adverse side effects during platelet transfusion. Therefore, optimization of preparation and storage of PC is still an active field of research. Shear-induced platelet activation is an unwanted side effect of the hard-spin (up to 5000g) step of centrifugation-based methods currently used in blood banks to prepare PC from whole blood samples. Here, we evaluated the effectiveness of an acoustic-based fractionation device for the isolation of human platelets from whole blood bags. The purity, activation status, and functionality of platelets isolated by acoustopheresis were compared with those of platelets isolated using a reference protocol known to produce limited platelet activation and consisting of two consecutive soft-spin centrifugations (120g and 1200g). Platelet concentration and purity were determined using an automated hematology analyzer. Platelet activation status and platelet reactivity to collagen and thrombin were assessed in flow cytometry by measurement of surface expression of P-selectin and activated integrin αIIbβ3. The ability of isolated platelets to incorporate into a thrombus when transfused to NOD/SCID mice was investigated by intravital microscopy using the ferric chloride-induced thrombosis model. Blood fractionation by acoustophoresis led to the elimination of more than 80% of red blood cells and leukocytes from the platelet fraction, whose mean purity was of 92.8 ± 12.8%. The activation status and reactivity to collagen and thrombin of acoustophoresis-isolated platelets were similar to those of platelets isolated by soft-spin centrifugation. Finally, acoustophoresis-isolated platelets were tethered, adhered to the vessel wall, and incorporated into a growing thrombus following ferric chloride-induced vascular injury. Together, our results indicate that acoustophoresis is a suitable method for the isolation of human platelets with minimal platelet activation and preservation of platelet function.

Monitoring storage induced changes in the platelet proteome employing label free quantitative mass spectrometry

Shelf life of platelet concentrates is limited to 5-7 days due to loss of platelet function during storage, commonly referred to as the platelet storage lesion (PSL). To get more insight into the development of the PSL, we used label free quantitative mass spectrometry to identify changes in the platelet proteome during storage. In total 2501 proteins were accurately quantified in 3 biological replicates on at least 1 of the 7 different time-points analyzed. Significant changes in levels of 21 proteins were observed over time. Gene ontology enrichment analysis of these proteins revealed that the majority of this set was involved in platelet degranulation, secretion and regulated exocytosis. Twelve of these proteins have been shown to reside in α-granules. Upon prolonged storage (13-16 days) elevated levels of α-2-macroglobulin, glycogenin and Ig μ chain C region were identified. Taken together this study identifies novel markers for monitoring of the PSL that may potentially also be used for the detection of "young" and "old" platelets in the circulation.

Sphingosine-1-phosphate improves endothelialization with reduction of thrombosis in recellularized human umbilical vein graft by inhibiting syndecan-1 shedding in vitro

Sphingosine-1-phosphate (S1P) has been known to promote endothelial cell (EC) proliferation and protect Syndecan-1 (SDC1) from shedding, thereby maintaining this antithrombotic signal. In the present study, we investigated the effect of S1P in the construction of a functional tissue-engineered blood vessel by using human endothelial cells and decellularized human umbilical vein (DHUV) scaffolds. Both human umbilical vein endothelial cells (HUVEC) and human cord blood derived endothelial progenitor cells (EPC) were seeded onto the scaffold with or without the S1P treatment. The efficacy of re-cellularization was determined by using the fluorescent marker CellTracker CMFDA and anti-CD31 immunostaining. The antithrombotic effect of S1P was examined by the anti-aggregation tests measuring platelet adherence and clotting time. Finally, we altered the expression of SDC1, a major glycocalyx protein on the endothelial cell surface, using MMP-7 digestion to explore its role using platelet adhesion tests in vitro. The result showed that S1P enhanced the attachment of HUVEC and EPC. Based on the anti-aggregation tests, S1P-treated HUVEC recellularized vessels when grafted showed reduced thrombus formation compared to controls. Our results also identified reduced SDC1 shedding from HUVEC responsible for inhibition of platelet adherence. However, no significant antithrombogenic effect of S1P was observed on EPC. In conclusion, S1P is an effective agent capable of decreasing thrombotic risk in engineered blood vessel grafts.

STATEMENT OF SIGNIFICANCE

Sphingosine-1phosphate (S1P) is a low molecular-weight phospholipid mediator that regulates diverse biological activities of endothelial cell, including survival, proliferation, cell barrier integrity, and also influences the development of the vascular system. Based on these characters, we the first time to use it as an additive during the process of a small caliber blood vessel construction by decellularized human umbilical vein and endothelial cell/endothelial progenitor. We further explored the function and mechanism of S1P in promoting revascularization and protection against thrombosis in this tissue engineered vascular grafts. The results showed that S1P could not only accelerate the generation but also reduce thrombus formation of small caliber blood vessel.

Flow cytometry analysis of platelet populations: usefulness for monitoringthe storage lesion in pooled buffy-coat platelet concentrates

BACKGROUND

Early detection of the platelet storage lesion is still a challenge in transfusion practice. Using flow cytometry, we evaluated the appearance of the storage lesion, based on the expression of platelet activation markers, in total platelets and platelet populations.

MATERIALS AND METHODS

Buffy-coat-derived platelet concentrates were stored under standard conditions for 5 days. The expression of activation antigens CD42b, CD36, CD62p and phosphatidylserine on total platelets and populations of small, medium-sized and large platelets was analysed by flow cytometry on storage days 1, 3 and 5.

RESULTS

The activation/lesion on total platelets and each platelet population was detected on storage day 3, by the increased expression of CD36. On the same day, increased expression of CD42b and CD62p was detected, but only on large platelets. Small and medium-sized platelets had increased CD62p expression only on day 5. Externalisation of phosphatidylserine was not detected.

DISCUSSION

Evaluation of the level of expression of various activation markers on different platelet populations could be an additional valid analysis in cell quality control of platelet concentrates, and in the assessment of novel approaches to platelet concentrate manipulation.

Quality Assessment of Established and Emerging Blood Components for Transfusion

Blood is donated either as whole blood, with subsequent component processing, or through the use of apheresis devices that extract one or more components and return the rest of the donation to the donor. Blood component therapy supplanted whole blood transfusion in industrialized countries in the middle of the twentieth century and remains the standard of care for the majority of patients receiving a transfusion. Traditionally, blood has been processed into three main blood products: red blood cell concentrates; platelet concentrates; and transfusable plasma. Ensuring that these products are of high quality and that they deliver their intended benefits to patients throughout their shelf-life is a complex task. Further complexity has been added with the development of products stored under nonstandard conditions or subjected to additional manufacturing steps (e.g., cryopreserved platelets, irradiated red cells, and lyophilized plasma). Here we review established and emerging methodologies for assessing blood product quality and address controversies and uncertainties in this thriving and active field of investigation.

High-throughput acoustic separation of platelets from whole blood

Platelets contain growth factors which are important in biomedical and clinical applications. In this work, we present an acoustic separation device for high-throughput, non-invasive platelet isolation. In particular, we separated platelets from whole blood at a 10 mL min(-1) throughput, which is three orders of magnitude greater than that of existing acoustic-based platelet separation techniques. Without sample dilution, we observed more than 80% RBC/WBC removal and platelet recovery. High throughput, high separation efficiency, and biocompatibility make this device useful for many clinical applications.

Evaluation of the role of the GPIb-IX-V receptor complex in development of the platelet storage lesion

BACKGROUND AND OBJECTIVES

In mice, loss of sialic acid resulting in shedding of glycoprotein (GP) Ibα and GPV has been linked to platelet survival. The aim of this study was to determine whether loss of sialic acid and the GPIb-IX-V complex contributes to development of the platelet storage lesion (PSL) in human platelet concentrates (PCs).

MATERIALS AND METHODS

PCs (stored in plasma (with or without Mirasol treatment); PAS-C or PAS-E) were stored at room temperature. Flow cytometry was used to monitor membrane expression of the GPIb-IX-V complex, CD62P, surface glycans and PS exposure. The functionality of stored platelets was determined employing aggregometry and ristocetin-induced VWF binding.

RESULTS

Storage time of PCs in blood banks is limited to 7 days. During this time period, a minor but gradually increasing subpopulation of GPIbα-negative platelets was observed. Also, ristocetin-induced VWF binding was impaired in a small population of platelets. Mean surface expression of GPIbα and GPV remained stable until day 9, whereas CD62P expression increased; also a rapid decrease in ADP-induced aggregation was observed for PAS-C, PAS-E and Mirasol-treated PCs. Upon prolonged storage (>9 days), a slow decline in surface expression of GPIbα and GPV was observed; no major changes were observed in surface sialylation with the exception of Mirasol-treated platelets.

CONCLUSION

In a small population of stored platelets, changes in GPIbα occur from day 2 onwards. Loss of sialic acid and subsequent shedding of GPIbα and GPV is not an early event during the development of the PSL.

Assessment of canine autologous platelet-rich plasma produced with a commercial centrifugation and platelet recovery kit

OBJECTIVES

To characterize the cellular composition (platelets, erythrocytes, and leukocytes) and confirm reproducibility of platelet enrichment, as well as determine the platelet activation status in the final product of a commercial platelet-rich plasma kit using canine blood.

METHODS

Venous blood from 20 sedated client-owned dogs was used to prepare platelet-rich plasma (PRP) from a commercial kit. Complete blood counts were performed to determine erythrocyte, leukocyte, and platelet numbers in both whole blood (WB) and resultant PRP. The WB and PRP samples from jugular (fast collection) and cephalic (slow collection) venipuncture were also compared. P-selectin externalization was measured in WB and PRP samples from 15 of 20 dogs.

RESULTS

This commercial kit produced an average percent recovery in platelets of 64.7 ± 17.4; erythrocytes of 3.7 ± 0.8, and leukocytes of 31.6 ± 10.0. Neutrophil, monocyte, and lymphocyte percent recovery was 19.6 ± 7.2, 44.89 ± 19.8, and 57.5 ± 10.6, respectively. The recovery of platelets from jugular venipuncture (59.7 ± 13.6%) was lower than from cephalic recovery (68.8 ± 19.1%). The mean percent P-Selectin externalization for WB, PRP, and PRP with thrombin was 25.5 ± 30.9, 4.5 ± 6.4, and 90.6 ± 4.4 respectively.

CLINICAL SIGNIFICANCE

Cellular reproducibility of this kit was confirmed and platelets were concentrated within autologous serum. Additionally, measurements of P-selectin externalization showed that platelets are inactive in PRP unless stimulated to degranulate.

The association between platelet transfusion and idiopathic pneumonia syndrome is unaffected by platelet product type

BACKGROUND

Methods used to produce platelet (PLT) components, pooling of PLT-rich plasma (PRP-PLT) and apheresis (AP-PLT), may variably contribute to the pathogenesis and severity of idiopathic pneumonia syndrome (IPS).

STUDY DESIGN AND METHODS

We performed a retrospective cohort study of 906 allogeneic hematopoietic cell transplant recipients to examine associations between PLT product type and risks of developing IPS and dying after IPS onset. Proportional hazards models included separate terms for the sum of all PLT transfusions and the sum of PRP-PLT units received in the 3 or 7 days before IPS onset. Similarly constructed models analyzed the outcome of time to death after IPS onset. All analyses were adjusted for known IPS risk factors.

RESULTS

Patients received a median of three PRP-PLT transfusions (interquartile range [IQR], 0-6) and five AP-PLT transfusions (IQR, 1-13) while at risk for IPS. Seventy-five patients (8%) developed IPS by Posttransplant Day 120. The proportion of PRP-PLT transfusions was not associated with risk of developing IPS (3-day hazard ratio [HR] 0.98, 95% CI 0.74-1.29, p = 0.86; 7-day HR 1.00, 95% CI 0.86-1.15, p = 0.95) or dying after IPS onset (3-day HR 0.99, 95% CI 0.75-1.31, p = 0.97; 7-day HR 0.98, 95% CI 0.78-1.12, p = 0.47).

CONCLUSION

The association between PLT transfusions and risk of developing IPS or dying after IPS onset does not differ according to PLT product type. Further research is required to identify potentially modifiable steps in PLT component production that contribute to IPS.

Evaluation of store lesion in platelet obtained by apheresis compared to platelet derived from whole blood and its impact on the in vitro functionality

Platelet units for transfusion purposes are obtained manually from whole blood or by apheresis, in an automated process. In both methods, platelets during storage present a characteristics grouped under the name "storage lesion" that are associated with adverse effects on platelet units. Oxidative stress has been claimed to be one of major causes, leading to activation and apoptosis processes affecting their post transfusion functionality. In this work, we observed an association between apheresis and a reduced presence of oxidative stress and better results in functional markers in stored platelets, compared to manually obtained platelets. Then, apheresis which would ensure a greater number of functional platelets during the 5 days of storage, compared to concentrates obtained from whole blood.

Stem cells, megakaryocytes, and platelets

PURPOSE OF REVIEW

Stem cells are an important tool for the study of ex-vivo models of megakaryopoiesis and the production of functional platelets. In this manuscript, we review the optimization of megakaryocyte and platelet differentiation and discuss the mechanistic studies and disease models that have incorporated stem cell technologies.

RECENT FINDINGS

Mechanisms of cytoskeletal regulation and signal transduction have revealed insights into hierarchical dynamics of hematopoiesis, highlighting the close relationship between hematopoietic stem cells and cells of the megakaryocyte lineage. Platelet disorders have been successfully modeled and genetically corrected, and differentiation strategies have been optimized to the extent that utilizing stem cell-derived platelets for cellular therapy is feasible.

SUMMARY

Studies that utilize stem cells for the efficient derivation of megakaryocytes and platelets have played a role in uncovering novel molecular mechanisms of megakaryopoiesis, modeling and correcting relevant diseases, and differentiating platelets that are functional and scalable for translation into the clinic. Efforts to derive megakaryocytes and platelets from pluripotent stem cells foster the opportunity of a revolutionary cellular therapy for the treatment of multiple platelet-associated diseases.

Hemostatic function of apheresis platelets stored at 4°C and 22°C

INTRODUCTION

Platelet refrigeration decreases the risk of bacterial contamination and may preserve function better than standard-of-care room temperature (RT) storage. Benefits could include lower transfusion-related complications, decreased costs, improved hemostasis in acutely bleeding patients, and extended shelf life. In this study, we compared the effects of 22°C and 4°C storage on the functional and activation status of apheresis platelets.

METHODS

Apheresis platelets (n = 5 per group) were stored for 5 days at 22°C with agitation (RT) versus at 4°C with agitation (4°C + AG) and without (4°C). Measurements included platelet counts, mean platelet volume, blood gas analytes, aggregation response, thromboelastography, thromboxane B2 and soluble CD40 ligand release, activation markers, and microparticle formation.

RESULTS

Sample pH levels were within acceptable limits for storage products (pH 6.2-7.4). Platelet glucose metabolism (P < 0.05), aggregation response (adenosine diphosphate: RT 0; 4°C + AG 5.0 ± 0.8; 4°C 5.6 ± 0.9; P < 0.05), and clot strength (maximum amplitude: RT 58 ± 2; 4°C + AG 63 ± 2; 4°C 67 ± 2; P < 0.05) were better preserved at 4°C compared with RT storage. Refrigerated samples were more activated compared with RT (P < 0.05), although thromboxane B2 (P < 0.05) and soluble CD40 ligand release (P < 0.05) were higher at RT. Agitation did not improve the quality of 4°C-stored samples.

CONCLUSIONS

Apheresis platelets stored at 4°C maintain more viable metabolic characteristics, are hemostatically more effective, and release fewer proinflammatory mediators than apheresis platelets stored at RT over 5 days. Given the superior bacteriologic safety of refrigerated products, these data suggest that cold-stored platelets may improve outcomes for acutely bleeding patients.

Platelet adhesion changes during storage studied with a novel method using flow cytometry and protein-coated beads

The aim of the present study was to set up and evaluate a novel method for studies of platelet adhesion and activation in blood and platelet suspensions such as platelet concentrate (PC) samples using protein-coated polystyrene beads and flow cytometry. To demonstrate its usefulness, we studied PCs during storage. PCs were prepared by aphaeresis technique (n = 7). Metabolic variables and platelet function was measured on day 1, 5, 7 and 12 of storage. Spontaneous and TRAP-6-induced adhesion to fibrinogen- and collagen-coated beads was analyzed by flow cytometry. P-selectin and phosphatidyl serine (PS) expression was assessed on platelets bound to beads as well as on non-adherent platelets. Platelet adhesion to fibrinogen beads had increased by day 12 and adhesion to collagen beads at day 7 of storage (p < 0.05). TRAP-6 stimulation significantly increased the platelet adhesion to fibrinogen beads (p < 0.05) as well as the P-selectin and PS exposure on platelets bound to beads (p < 0.01) during the first 7 days of storage, but by day 12, significant changes were no longer induced by TRAP-6 stimulation. We demonstrate that our adhesion assay using protein-coated polystyrene beads can be used to assess the adhesion properties of platelets during storage without the addition of red blood cells. Therefore it may offer a useful tool for future studies of platelet adhesive capacity in transfusion medicine and other settings.

Elevated levels of procoagulant plasma microvesicles in dialysis patients

Cardiovascular (CV) death remains the largest cause of mortality in dialysis patients, unexplained by traditional risk factors. Endothelial microvesicles (EMVs) are elevated in patients with traditional CV risk factors and acute coronary syndromes while platelet MVs (PMVs) are associated with atherosclerotic disease states. This study compared relative concentrations of circulating MVs from endothelial cells and platelets in two groups of dialysis patients and matched controls and investigated their relative thromboembolic risk. MVs were isolated from the blood of 20 haemodialysis (HD), 17 peritoneal dialysis (PD) patients and 20 matched controls. Relative concentrations of EMVs (CD144(+ ve)) and PMVs (CD42b(+ ve)) were measured by Western blotting and total MV concentrations were measured using nanoparticle-tracking analysis. The ability to support thrombin generation was measured by reconstituting the MVs in normal plasma, using the Continuous Automated Thrombogram assay triggered with 1µM tissue factor. The total concentration of MVs as well as the measured sub-types was higher in both patient groups compared to controls (p<0.05). MVs from HD and PD patients were able to generate more thrombin than the controls, with higher peak thrombin, and endogenous thrombin potential levels (p<0.02). However there were no differences in either the relative quantity or activity of MVs between the two patient groups (p>0.3). Dialysis patients have higher levels of circulating procoagulant MVs than healthy controls. This may represent a novel and potentially modifiable mediator or predictor of occlusive cardiovascular events in these patients.

Growth factor release from platelet concentrates: analytic quantification and characterization for clinical applications

BACKGROUND AND OBJECTIVES

Clinical use of plasma rich in growth factors requires biochemical product control. We aimed to measure and modulate concentrations of growth factors in solutions deriving from platelet apheresis or whole blood.

MATERIALS AND METHODS

Growth factor concentrations were measured 5', 10', 20', 30', 60' after CaCl2 was added at 40°C to platelet-apheresis products (n = 39) or after 60' in platelet concentrates from whole blood (n = 13). Growth factor release was also obtained in platelet apheresis a) by incubation at 22°C or 40°C for 10' or 30' (n = 4); b) by repeated freeze-thaw (n = 9).

RESULTS

Fibroblast growth factor (FGF), platelet-derived growth factor (PDGF) isoforms AA and AB and transforming growth factor beta (TGF-β) concentrations (pg/10(9 ) plt) were 25-60% higher in growth factors solutions from whole blood compared to platelet apheresis. Vascular endothelial growth factor (VEGF), TGF-β and PDGF isoforms were released early (5-10') during incubation: TGF-β concentration increased also at 30'. FGF and epidermal growth factor (EGF) were released only after 30'. Incubation at 40°C/10' increased VEGF (+70%) and decreased EGF (-30%) and PDGF-BB (-50%) versus 22°C/30'. Shock significantly increased TGF-β (1.6-fold), EGF (1.5-fold), FGF (4.5-fold) and lowered PDGF isoforms (0.2- to 0.5-fold) versus prolonged incubation at 40°C.

CONCLUSION

Platelets from platelet apheresis and whole-blood release all investigated growth factors. The release can be regulated controlling incubation time and/or temperature and performing cell lysis.

Tissue Factor Expression on Platelet Surface during Preparation and Storage of Platelet Concentrates

BACKGROUND

Tissue factor (TF), the main activator of blood coagulation, is expressed on platelet surface and, together with procoagulant phospholipids, contributes to the global coagulation potential of these blood components. The present study evaluated, for the first time, the expression of TF on platelet surface during preparation and storage of platelet concentrates (PC) for transfusional use.

METHODS

Platelet TF was measured by flow cytometry in healthy donor whole blood (WB) and in pooled buffy-coat-derived PC on the day of preparation and up to 4 days of storage in parallel with classical markers of platelet activation, i.e., fibrinogen, P-selectin, and glycoprotein GPIIb. Data were analyzed according to donor age and blood ABO group.

RESULTS

TF was detected on whole blood platelets and was found highest in O donors. Compared to whole blood, platelet surface TF was higher upon PC preparation and further increased during storage. The rise in TF levels positively correlated with the elevations of the other platelet markers.

CONCLUSIONS

Our findings show that platelet surface TF is maintained in PC obtained by the pooled buffy coat method. Further studies are warranted to investigate a possible correlation between TF levels and the hemostatic response of the platelet transfusion recipient.

A rest period does not affect in vitro storage properties in apheresis platelets collected from the buffy coat layer

BACKGROUND

A previous study demonstrated that several in vitro storage properties of apheresis platelets (PLTs) that are isolated by sedimentation against the collection container and subsequently resuspended can benefit from a rest period before continuous agitation. This study examines whether the in vitro storage properties of apheresis PLTs isolated by collection from the buffy coat layer benefit from a rest period before agitation.

STUDY DESIGN AND METHODS

Freshly collected apheresis PLTs (Trima, GambroBCT) were divided into five 60-mL aliquots. One aliquot was immediately placed on a flat-bed agitator; the other aliquots were held on a laboratory bench for 1, 2, 4, and 6 hours before continuous agitation. Samples were obtained on Days 1, 5, and 7 for standard in vitro PLT assays. The experiment was repeated 12 times.

RESULTS

For each sampling day, no significant differences were observed in aliquots held with or without a rest period for any of the following PLT properties: PLT content, mean PLT volume, pH, pCO2, bicarbonate, glucose, lactate, hypotonic shock response, extent of shape change, aggregation, morphology, CD62P, CD63, and CD42b. Although regression analysis identified several in vitro properties whose mean levels appeared to improve with increasing length of the rest period, maximum differences in mean levels were small (<6%).

CONCLUSION

The in vitro storage properties of Trima apheresis PLTs isolated from the buffy coat layer do not benefit from a rest period.

Development of a quality monitoring program for platelet components: a report of the first four years' experience at Canadian Blood Services

BACKGROUND

A quality monitoring program (QMP) for platelet concentrates (PCs) was implemented at Canadian Blood Services (CBS) to improve standards and to better understand platelet (PLT) products by supplementing routine quality control (QC).

STUDY DESIGN AND METHODS

Annual surveys of PCs from CBS production sites were conducted, with four completed to date (QMP Cycles 1-4) spanning two different PC production methods: PLT-rich plasma (PRP) and buffy coat (BC). Randomly selected PCs were sent to a central laboratory and tested 1 day after expiry. An expanded panel of tests including CD62P expression by flow cytometry, mean PLT volume, PLT count and morphology, extent of shape change, and PLT metabolic parameters, were applied.

RESULTS

QMP data on the implementation of the BC production method across CBS indicated that BC PCs have less variable in vitro quality measures than PRP PCs. For the QC parameters pH and PLT count per unit, the range of mean values from each site for QMP 3 and 4 fell well within the range defined by regulatory standards, a first step in defining quality benchmarks for PCs. Of the extended panel of quality parameters, CD62P expression was the most sensitive indicator of change and identified an issue with the implementation of the BC PC production method at one site, which was subsequently remedied.

CONCLUSION

A QMP was found to be useful to monitor production processes across sites and highlights best practice approaches while deepening understanding of the quality of PLT products at CBS.

Efficient removal of platelets from peripheral blood progenitor cell products using a novel micro-chip based acoustophoretic platform

Background

Excessive collection of platelets is an unwanted side effect in current centrifugation-based peripheral blood progenitor cell (PBPC) apheresis. We investigated a novel microchip-based acoustophoresis technique, utilizing ultrasonic standing wave forces for the removal of platelets from PBPC products. By applying an acoustic standing wave field onto a continuously flowing cell suspension in a micro channel, cells can be separated from the surrounding media depending on their physical properties.

Study Design and Methods

PBPC samples were obtained from patients (n = 15) and healthy donors (n = 6) and sorted on an acoustophoresis-chip. The acoustic force was set to separate leukocytes from platelets into a target fraction and a waste fraction, respectively. The PBPC samples, the target and the waste fractions were analysed for cell recovery, purity and functionality.

Results

The median separation efficiency of leukocytes to the target fraction was 98% whereas platelets were effectively depleted by 89%. PBPC samples and corresponding target fractions were similar in the percentage of CD34+ hematopoetic progenitor/stem cells as well as leukocyte/lymphocyte subset distributions. Median viability was 98%, 98% and 97% in the PBPC samples, the target and the waste fractions, respectively. Results from hematopoietic progenitor cell assays indicated a preserved colony-forming ability post-sorting. Evaluation of platelet activation by P-selectin (CD62P) expression revealed a significant increase of CD62P+ platelets in the target (19%) and waste fractions (20%), respectively, compared to the PBPC input samples (9%). However, activation was lower when compared to stored blood bank platelet concentrates (48%).

Conclusion

Acoustophoresis can be utilized to efficiently deplete PBPC samples of platelets, whilst preserving the target stem/progenitor cell and leukocyte cell populations, cell viability and progenitor cell colony-forming ability. Acoustophoresis is, thus, an interesting technology to improve current cell processing methods.

BCL2/BCL-X(L) inhibition induces apoptosis, disrupts cellular calcium homeostasis, and prevents platelet activation

Apoptosis in megakaryocytes results in the formation of platelets. The role of apoptotic pathways in platelet turnover and in the apoptotic-like changes seen after platelet activation is poorly understood. ABT-263 (Navitoclax), a specific inhibitor of antiapoptotic BCL2 proteins, which is currently being evaluated in clinical trials for the treatment of leukemia and other malignancies, induces a dose-limiting thrombocytopenia. In this study, the relationship between BCL2/BCL-X(L) inhibition, apoptosis, and platelet activation was investigated. Exposure to ABT-263 induced apoptosis but repressed platelet activation by physiologic agonists. Notably, ABT-263 induced an immediate calcium response in platelets and the depletion of intracellular calcium stores, indicating that on BCL2/BCL-X(L) inhibition platelet activation is abrogated because of a diminished calcium signaling. By comparing the effects of ABT-263 and its analog ABT-737 on platelets and leukemia cells from the same donor, we show, for the first time, that these BCL2/BCL-X(L) inhibitors do not offer any selective toxicity but induce apoptosis at similar concentrations in leukemia cells and platelets. However, reticulated platelets are less sensitive to apoptosis, supporting the hypothesis that treatment with ABT-263 induces a selective loss of older platelets and providing an explanation for the transient thrombocytopenia observed on ABT-263 treatment.

The effect of a leukodepletion model on the activation stage of platelets

The preparation of thrombocyte concentrates with filtration before storage (in-line) makes it possible to avoid the presence of mononuclear cells in the concentrate and proinflammatory cytokines. Therefore, this filtration may result with decreased activation of trombocyte receptors in vitro, which may improve therapeutic efficiancy. Methods. We compared two groups, each with 30 therapeutic doses of concentrated thrombocytes. We prepared the first group using the classic model from the buffy coat and the other with concentrated thrombocyte samples filtrated during sampling, so-called in-line, with the WBC filter Imuflex (Terumo). Mononuclear cells (MNC), thrombocyte, and erythrocyte counts in the units of concentrated thrombocytes were obtained on an automatic cell counter, and we used flow cytometry to measure the expression of surface thrombocyte receptors. The results demonstrated that the trombocytes prepared with pre-storage filtration contained a very low level of mononuclear cells and markedly reduced trombocyte receptors. Conclusion. The number of MNC and expression of surface thrombocyte receptors were markedly lower in the concentrated thrombocyte units prepared with in-line filtration. The thrombocytes prepared in this way contain fewer mononuclear cells, are of higher quality, are more functional, and may produce a better therapeutic effect in vivo.